Telephone system



July 4, 1939. l R.v. L. HARTLEY 2,164,325

TELEPHONE SYSTEM R. u L. HARTLEV By MSNM A T TORNE V July 4, 1939. R. v. L. HARTLEY 2,164,325

TELEPHONE SYSTEM Filed Aug. 51, 1937 4 sheets-sheet :s

- /NVENTO R. u L. HARM-EV www 'ATTORNEY l July 4, 1939. R. v. 1 HARTLEY TELEPHONE SYSTEM Filed Aug. 51, 1957 4 Smets-'sheet 4 /NVENTOR R. u L. HARTLEV r A T TORNE V Patented July Y4, 193.9

lomiso STATES PATENT; ori-fics Ralph v. L. Hartley, summit, NJ., assignmo` Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August a1. 1931. serial No. 161.1411` 1o claims. (c1. 11s-1s) 5 The objects of the invention are to simplify the acts necessary on the part of subscribers and operators in transmitting and in recording signals, such as telephone designations; to' improve'the eiiciency and to increase the speed of operation of the equipment; and otherwise to improve systems of this kind.

Systems have been proposed heretofore in which the designations 'of called linesl or trunk circuits are transmitted from one point to anu other by means of currents of different frequencies, the frequencies ysingly or in combination serving to characterize the dierent numerals or other characters of the designation.v v

According to the present invention advantages are secured over these prior systems by providingthe substation of a telephone line with an oscillatory device vwhich may be adjusted by the vsubscriber to oscillate at different resonant frequencies characterizing the different digits of thev wanted number. The oscillatory device may be energized by current of a relatively high frequency supplied over the line from thecentral office to produce in the line a resultant beat frequency current which is utilized at the central otlice to selectively operate the designation registers. The beat frequency characterizing the different digits of a wanted designation may `be separated at the central ciiice by selective filters to selectively operate the central oillce registers, which in turn control the selective operation of theswitches in the establishment of the ldesired connection. If desired the beat frequencyl c'ur- I 5o the natural period of which isadjusted by deslignatlon keys, and which vibrates in the field of an electromagnetic device to produce lthe currents in the subscribers line.

Another feature is a system of the character above described in which the oscillating device ments of these devices with currents of `frequenat the subscribers station consists of an electrical circuit having reactance elements therein whichare varied by the designation keys to obtain different natural frequenciesof oscillation of the circuit, these resonant frequencies identi- 5 l fying the different characters of a subscribers designation. The. oscillating circuit is coupled to the subscribers line by means of'a transformer which is preferably designed Vto operate on the curved portion of its flux density characteristic. m

'In this way the current in the line supplied from appended claims.

In the drawingsFigs. l, 2 and 3, when arranged in the order shown in Fig. 6, illustrate an autom'atic telephone system embodying the principles of the invention.

Fig. 1 shows a subscribers station and illustrates the structure of one form of the number transmitter; 30

Figs, 2 and 3 disclose the central omce in which Athe subscribers line terminates and shows in detail the number recording mechanism;

. Fig. 4 illustrates an alternative form of the number sending device for use at the subscribers statin; and I F'lg. 5.shows a modification of the tuned circuit used in the' sending mechanism of Fig. 4.

Experiments have shown that vibratory and oscillatory devices, such as vibrating reeds and s oscillating. circuits, may be caused to oscillate at'their' naturalperiods with considerable ease and with `the expenditure of relatively small amounts of energy by exciting the driving elecies much higher than the natural vibration frequencies of the devices themselves. By taking advantage of this fact inthe present system it is possible to drivelan oscillatory device at a subscribers substation atanyone of a number of relatively low frequencies, each of which can vbe selected to characterize a number or letter of a subscribers telephone designation, by p roviding a source of relatively high frequency current at the central office and applying it to the `5gg line for-the purposeof exciting the oscillatory device at the substation. If the oscillatory device at the substation is of the type shown in Fig. 1, comprising a vibrating reed having a magnetic element arranged in the field of the exciting coil, the mechanical vibration of this reed in said field produces in the coil and in the line currents oi two principal frequencies. One of these is the sum of the frequencies of the exciting current and of the vibrating reed, and the other is the difference of these two frequencies. By properly designing the impedance of the line, it is possible to substantially suppress the sumfrequency currents, leaving the difference-frequency currents predominating in the line for transmitting the telephone designations to the central oilice. When the sending mechanisms shown in Fig. 4 or in Fig. 5 are used at the substation the vibrating reed is replaced by an oscillatory electric circuit comprising a variable reactance. This circuit-is coupled to the subscribers line by means of a transformer, and by operating the transformer on the non-linear portion of its flux density characteristic, the circuit is caused to oscillate by the presence of the high frequency current flowing in the subscribers line. The oscillatory circuit operating at its natural frequency causes the sum and difference frequency currents to flow in the subscribers line. These currents, like those produced by the sending device of Fig. l, are utilized as will be explained hereinafter to record the wanted numbers at the central office.

netic element orv armature |02.

Before proceeding to the operation of the system, a description will be given of the equipment used, including the structure of thesubstation sending mechanisms and the receiving and register circuits of the central omce.

The sender or transmitter shown in Fig. 1 comprises a vibratorygreed |00 secured to the mounting |0l and equipped at its free end with a mag'- The armature |02 lies between the pole-pieces of the core |03 on which an exciting coil |04 is wound. The sender also includes a keyboard having the 'necessary number of individual keys to characterize the numerals and letters which make up the designations of subscribers lines. Five of these keys are illustrated, keys |05, |06, |01, |03 `and |09, but as many more as are necessary may be provided. The key levers are arranged perpendicularly with respect to the reed |00. They are pivoted on rod ||0 and extend so that their free ends lie in close proximity to the vibratory reed |00. Each of these key levers is provided with a notch .or slot so arranged that when the key is tilted the notch encompasses the reed |00 at a point along the length of the reed which depends upon the particular key involved. These notches are tapered so that the reed is wedged and held firmly'in position by the operated key. For example, if key |05 is depressed, the key lever rotates about the rod I0 and the V-shaped notch ||2 near the end of said lever engages the reed |00 and holds it firmly against 'vibration at the point of engagement. The effect of this is to shorten the vibratory portion of the reed by a different digits or characters, determine the efu fective length and correspondingly the frequency.

, number of characters.

at which the reed will vibrate during the time it is engaged and held by any one of these keys. In addition to these elements the transmitting mechanism is provided with a cam bar |`|5 for operating the circuit contact springs H8, and ||8. 'I'he bar ||5 is provided with a series of cams H9, |20, |2I, |22, |23, etc., one for each of the several key levers. Normally the cam bar i I5 is held against the stop member |24 by means of the retractile spring |25, in this position holding the contact springs ||6 and ||8 closed and holding the contact springs and ||8 open. When any one of the keys is depressed its lever engages the corresponding cam on the bar ||5 and forces vthe bar against the spring |25, permitting contact spring ||6 to disengage spring ||8 and permitting spring ||8 to engage spring The purpose of these springs will be described hereinafter.

'I'he keyboard structure used in the transmitter of Fig. 4 is similar to the one shown in Fig. 1. The vibratory reed and magnetic element is replaced with aseries `of circuit contacts and a tuned electrical circuit 400. The key levers 40|, 402, 403, 404 and 405 are pivoted on the rod l406 and their free ends serve to close the respective contacts 401, 408, 403, 4|0 and 4||. The oscila latory circuit 400 comprises a variable inductance 4|2, a capacitor 4|3, and the secondary winding of the transformer 4|4. Taps are taken from the inductance 4|2 at separated intervals and connected to the key operated contacts in such a way that the manipulation of any particular key closes the oscillatory circuit and includes therein a corresponding amount of the inductance. The primary winding of the transformer 4|4 is connected in the subscribers line. This transmitter, likethe one in Fig. 1, is provided with a cam bar 4|5 which serves'to operate the contact springs 4|6, 4|'|, 4|8 when any one of the keys is depressed. Y

The oscillatory circuit illustrated in Fig. 5 is similar to the one connected to the keyboard of Fig. 4 except that the key operated contacts serve to include variable amounts of capacity in circuit with a fixed inductance 4|9. The variadividual capacitors 420, 42|, 422, 423 and 424.

There will be as many of these individual ca pacitors as arenecessary to give the required The oscillatory circuit is connected to the line by means of a transformer 425.

A brief description will now be given of the `circuits and other equipment at the central office. The subscribers lines, each'of which is equipped with'a transmitter, such as those shown in Figs. l, 4 and 5, extend to the central ofilce and appear in line finder switches, such as the finder F. `The nder F serves to extend a calling line through to the first selector S and a sender .selector switch S| serves to extend the calling line to one 0i' the common central oice register senders, such as the one shown in the lower part of Fig. 2 and in Fig. 3. The common register sender includes a number of controlling relays and consists essentially of a frequency detecting and selecting mechanism and a number of relay registers. A source 200 of alternating current of suitable frequency is provided for supplying the subscribers line with the current to excite the substation transmitter. The alternating currents representing the designations are detected by a detector 20| amplified by an amplifler 202 and applied to a series of selective line, control the selective operation of the switches alters its, m, 20s, 200,201, etc. The number of digital registers will depend upon the size of the exchange area. It may be assumed that the designations in this particular area consist of two for the sake of simplicity. The'alternating cur- Y rents transmitted over the subscribers line and having frequencies representing the different designation characters are selected by the filters 203, 204, etc. and then cause the operation of the register relays to register these designation characters for further use in controlling the selective switches S, S-2-and S-3 to complete the connection through to the called subscribers line.

It will be understood, of course, that the register senders to which this invention has been applied include functions and equipment that have been omitted in the present disclosure for.v -the sake of simplicity. For example, the registers, having registered the code and numerical information received from the calling subscribers to extend the calling line to the called subscribers line either in the same or in the distant ofhce. For a better understanding of the manner in which the sender performs the functions that 'have been omitted in the present disclosure, reference is made to the patent to Raymond et al., No. '1,862,549'of -June 14, 1932 and to the patent to Stearn and Scudder, No. 1,395,977 of November l, 1921. Also the line finder and selector switches, illustrated diagrammatlcally in the drawings, may be of\any well-known types such as those disclosed in th`e Raymond et al. and in the Steam et' al. patents above noted.

The operation of the system will now be described, and for this purpose it may be assumed that the subscriber at station |20 wishes to call vthe subscriber at station 200. lAssume further that the designation of substation 200 is .AL-|234 and that the letter A is the equivalent of the numeral 2 and that the letter L is the equivalent of the numeral l5. When a subscriber at station |20 lifts his receiver to initiate the call, the line circuit is closed, and the finder F is started in operation in the usual way to seize the calling subscribers line. At the same time the sender selector S-v-I becomes effective to extend the calling subscribers line through to an idle sender. When, these operations have been completed, a circuit is closed from battery through the left winding ofthe line relay 209 in the sender, over vbrush lll, contact of spring 2|| on a controlling operates in this circuit and closes an obvious circuit for the slow-release relay 2|4. Relay 200 operatesonly in response to the flow of direct current through the operating circuit above traced and does not operate in response to the *brates would be of a much lower order. l high frequency current flowing through the'coil energy received from the alternating current source 200. Relay 2|4 closes an obvious circuit for'relay 300 and the latter relay.operates and extends the register operating conductors 00| through to the windings of the relays of the first code register A preparatory to the operation of these relays. At the same time a tone is sent from the tone device 2|5 to notify the. calling subscriber that the central office equipment is ready to receive the wanted designation.

The calling subscriber now manipulates 'the key |00 which characterizes the first letter A in the designation of the called subscriber. Key |00 tilts the lever |3| and fixes the 'period of vibration of the reed |00 to a frequency characterizing the 'letter A. At the same time thecam the circuit extending from the central oiilce now leads by Way of conductor |21 through-the coil |04, conductor |32, through the closed springs |||.and H8, conductor |29, thence through the substation switchhook contacts and over conductorl |30 as previously traced. The springs H6, Ill' and ||8 are so arranged that thecontinuity of the line circuitis preserved while the coil |04 is being introduced into said line circuit. Since the coil |04 is now included in the line circult, alternating current from the source 200 flows over this circuit and through the coil |04. As prevously'mentioned the 'current generated v by source 200 may have a frequency that is substantially higher than the natural frequency at which the reed |00 'vibrates While the invention is not so limited, a frequency of 1000 to 3000 cycles would be suitable for the source 200, whereas the frequencies at which the tuned reed vl- The output circuit of the detector aresultant current. having a frequency equal to that of the vibrating. reed |00. 'I'his resulting frequency current is amplified by a suitable amplifier 202 and is applied to the input circuits of theseveral lters `connected to the common circuit 2|6. 'I'here are as many of these filters as there are keys at the subscribers station andthe several filters are selectively designed to pass the frequencies corresponding to the respective keys at the substation. l

Therefore, the frequency resulting in the circuit 2|6 fromthe depression of key |06 is selectively passed 4by the filter 204 and is excluded by all other filters connected to the calling circuit. Current passing through the filter 204, and amplified, if necessary, causes the operation of'l re- 1 lay 2|1. The relay 2|`| operates common relay 2|8 and also operates relay 210. Relay 2|0 locks in a circuit from battery through its winding and.

left contact through the. make-before-break contact of relay2 I8 to ground at .the back contact of relay 220. Relay 2|9 at its right contact connects ground over conductor 22| through a contact of relay 300 to battery throughthe left winding of relay 302. Relay 0.02 operates to register the digit and prepares to lock in a circuit which will presently be'described. When the key |06 is released by the subscriber, contacts H6, ||1 and ||8 restore to normal and the coil |04 is removed from the line circuit. Current, therefore, ceases to flow in the filter circuit 204 and relay 2|1 releases, in turn releasing relay 2|0. Relay 2|8 in releasing closes its normal contacts before opening its front contacts. Therefore, before the locking circuit of relay 2|9is opened to permit the release of this relay, a holding circuit is closed as follows for the register relay 302: battery through the right winding and vcontacts of said register relay, Winding of relay 303, right normal contacts of relays 304, 305, 306, conductor 301, normal contacts of relay 2|8 to ground at the contact of relay 220. Relay 302 locks in this circuit, and relay 303 operates. When relay 2|8 fully releases, it opens the locking circuit of relay 2|9, and the latter relay releases. Relay 303 releases relay 300 to disconnect the common leads 30| from register A. Relay 303 also closes an operating circuit for relay 304. This circuit may be traced from battery through the winding of relay 304, normal left contact of relay 308 to vground at the contacts of relay 303. Relay 304 operates and extends the leads 30| through to the register B. The operated register relay 302 and relay 303 are now held in a circuit extending to ground through the front contacts of relay 303. 'I'he equipment is now in readiness for the receipt of the second digit ofthe called designation.

When the subscriber manipulates key |09 to transmit the second letter L, the effective vibratory length of theA reed is xed accordingly and the coil |04 is introduced into the line circuit. The vibration of reed |00 sets up a current of a corresponding frequency in the line, and this current is detected,ampliiied and applied to the common circuit 2I6. Since the detected current corresponds to the digit 5` it is passed by the selective network 201 and relays 222, 223 and 2|8,

operate. Relay 223 locks as above described and -applies ground to the common conductor 224,

which now extends through the Contact of relay 304 to operate the register relay 309 of the register B. When the subscriber releases the key ,|09, the coil l|04 is removed fromthe circuit and relays 222 and 2|8 release. Relay 2|8 in releasing closes a locking circuit for relay 309 traceable from the right winding and contact of said relay,

winding of relay 308, thence as previously traced over conductor 301 to ground. Relay 309 locks and relay 308 operates in this circuit before the holding circuit of relay 223 is broken. On the full release of relay 2|8, the holding circuit of relay 223 is open and thelatter relay releases. Relay 308 in operating causes release of relay-304 to disconnect the leads 30| from the register B. Relay 808 also closes an obvious circuit for the operation of relay 305 which extends theleads 30| through to the relays ofthe thousands register Th. The operated register relay 309 andrelay 308 now hold in a circuit jextending to ground through the right contacts of relay 308.

In a similar manner the depression of the keys corresponding to the four numerical digits cause register relay 3|0 of the thousands register.. 'Ihe depression of key |08 for the vhundreds digit 2 causes the operation ofa relay in the hundreds register corresponding to the relay 3|| of the thousands register. The manipulation of key` |01 for the tens digit causes the operation of two relays of the tens register corresponding to relays 3|0 and 3|| of the thousands register. Finally 'the manipulation of the key |08 for the units digit 4 causes the operation of units register relay 3I2.

In a manner well known in the art the operated register relays now serve to control the selective operations of the switches S, S-f-2 and S-3 to complete the extension of the calling line through to the called line 208. Thereafter the register sender is restored to normal and the parties converse with each other. At the end of conversation release of the switching equipment also takes place in the Well-known manner.

If desirable the subscribers station may be equipped with a number sender, utilizing a tuned electrical circuit for producing the characteristic currents in the line. Fig. 4 shows a sender of this kind, and this figure may be substituted for Fig. 1 to illustrate the system and its operation when the oscillatory circuit is used instead of the vibrating reed. The natural frequency of oscillation of the tuned circuit 400 is adjustable to the desired values by means of the keys. By properly designing the elements in the system including the coupling transformer 4|4, it is possible to have the transformer operating on the curved portion of its flux density characteristic. By so doing, the energy from the high frequency source 200 causes the circuit 400 to oscillate at any one of its natural frequencies as, determined by. the key depressed. The oscillation of the circuit 400 produces beat frequency currents in the line and these are detected and amplified and applied to the lters in the manner already described.

If desirable the variable inductance oscillating Vcircuit 400 may be replaced by the oscillating circuit of Fig. 5 which has a variable capacity.

What is claimed is: i

l. rI'he combination in a signaling system of a line having a station thereon, a source of alternating current of a given frequency, means for connecting said source to said line to supply current thereto, an oscillating device at said station responsive to current from said source to oscillate at its natural frequency, means for combining the frequency of said source and the frequency of said oscillating device to produce in said line a current of a resultant frequency, and means "sef lectively operable in response to said resultant frequency current.

2. 'I'he combination in a signaling system of a line having a station thereon, a source of alter.-

= nating current of a given frequency, means for connecting said sourcel to the line to supply current thereto, an oscillating device having a plurality of resonant frequencies and operable in response to current'owing in said line from said source to produce in the line currents of frequencies corresponding to said resonant frequencies, said resonant frequencies characterizing different characters of a designation, means to adjust said device to oscillate at any desired resonant frequency, and selective means responsive to the currents produced in said line for registering the characters in a designation.

3. In combination, a line having a station thereon, a source of alternating current of a relatively highvfrequency, means for connecting said source to said line to supply current thereto, an oscillating device at said station. voperable at a relatively low natural frequency in response to the high frequency current flowing in said line to produce in said line currents of beat frequency,

means for varying the natural frequency of-oscii-l lation of said oscillating device in accordance with the digits of a telephone designation to vary the frequency. of said beatv frequency currents, and means selectively responsive to said' beat frequency currents. to register the designation of ak telephone line.

4. -In combination, a line having a station thereon, a source of alternating current of relatively high frequency, means for connecting said source to said line Vto supply Acurrent thereto, an oscillating device at said station operable at a relatively low natural frequency in response to the high frequency current'fiowing.in said line to produce in said line currents of beat frequency,

means'for. varying the natural frequency of oscillation of 'said oscillating device in accordance.

with the digits of a telephonedesignation, 'means for detecting said beat frequency currents to obtain .currents of frequencies corresponding to the natural frequencies of said oscillating device, and 'means for utilizing said detected currents toregister' the designations of telephone lines.

o 5. The combination in a telephone system of a line having a` station thereon, a vibratingreed,`

-means for varyingthe natural period of said reed to characterize the digits of a telephone designation, means controlled over said line for driv` ing said reed, -means responsive to thefvibration bf said reed for producing in said line currents of corresponding frequencies, and means for utilizing said currents to control the selective exten-` sion of telephone connections. .i o

6. The combination in a telephone system of a 3| line, asingle vibratory reed, manual meansV for variably. determining the natural period of vibration of said reed to characterize the different digits of a telephone designation, a source of current for driving said lreed to producev in said line currents having frequencies corresponding to the vibration frequencies of said reed,l and means for utilizing the currents in said line to register the .l

designations of telephone lines.

7. The combination inv a communication system ofiazline havinga station thereon, an oscillatory circuit at said station Ahaving aplurality of natural periods-of oscillation, means for determining the oscillatory periods of said circuit tocharacterize the digits of a designation. a

source of alternating current for causing said circuit to oscillate, means for combining the frequencies produced in said oscillatory circuit with v rents 4thus obtained for controlling the station including a variable reactance, manual means vat the station for including variable amounts of said reactance in said oscillatory circuit to 'var'y the natural period of oscillation thereof, means for coupling said oscillatory circuit to said line to produce in said line currents having frequencies resulting from the combination of the frequencies ofoscillation'and the fre- 1 quency ofv said alternating current source, and

-means controlled by said resultant-frequency currents in said line for registering the designations of telephone subscribers. o

9. The combination in a telephone system of a line having a. substation thereon, a designation sender at the substation comprising .a single v'ibratory reed and keys for variably fixing the natural period vof vibration of said reed to characterizethe digits of a telephone designation, auto- .matic switches, a source of current for driving said Areed to'produce in said line currents having frequencies correspondingto the naturalperiods of vibration of said reed, and means responsive @to the currents flowing in 'said line for controlling the selective operation Vof said switchesto extend said line. e

10. 'I'he combination in a telephone system of 'a line' having a substation thereon, 'a -vibratory reed at said substation and designation keys for variably fixing the natural period of vibration of said reed to characterize the digits of a telephone designation, a source of alternating current connectedto said line for driving said reed, means for combining the frequencies of vibrationof said reed with the frequency of said source to'pro 'l duce in the line currents of resultant frequencies,

a lcentral office to which said line'extends, automatic switches in' said central oilice, 'means at the central. office for demodulating said resultant-frequency currents to obtain .currents having frequencies 'corresponding to the vibratoryperiods of said'reed, and means responsive .tothe ycurselective operation of said switches. y y

' RALPH V. L. HARTLEY. 

